TiddlyWiki is a “non-linear personal web notebook,” as well as an exemplar project in the open source community. It can be a note-taking or information-ordering system in a similar vein to Obsidian or Notion, although TiddlyWiki was launched back in 2004. It can also be thought of as producing a wiki with interactive components.
However, as I discovered to my cost, TiddlyWiki has never had a strong “start here,” because it is not tailored to one specific task. Obsidian, by comparison, has the advantage of a clear vision of what it does. TiddlyWiki bewilders you with options at first because it hasn’t been designed to be sold. The community focus is on adapting it to different use cases.
So I’m going to take the advice in this explainer and use TiddlyDesktop while mentioning that there are plenty of other arrangements. It is, after all, just HTML and JavaScript. Let’s get started…
Logseq is also open source but it does have plugins, it's extensible, and was launched in the last 5 years, not 20.
The caveat is that it's more of a Roam alternative, so it works for the many people who use Obsidian/Notion as a powerful outliner, but it might fall a bit short as a wiki. I'd still favour it over TW though.
That's why I did not use Logseq at first, but tbh, I see bo problem in building a knowledge base with Logseq. It's working well for me.